1. Field of the Invention
The present invention relates to improvements to an engine exhaust assembly. In particular, the present invention relates to an engine exhaust assembly for a motorcycle.
2. Description of Related Art
Engine exhaust assemblies for motorcycles are known, for example, from (1) Japanese Patent Laid-open No. Hei. 10-238334, entitled 4-cycle engine, and (2) Japanese Utility Model Laid-open No. Hei. 2-22617, entitled Engine Exhaust Assembly.
In the above mentioned document (1) according to FIG. 1 and FIG. 2 of that publication, an exhaust pipe 40 is connected to an exhaust passageway 14 of a cylinder head 4. Furthermore, a variable valve 41 having a cutaway section 41a is provided in the exhaust passageway side of the exhaust pipe 40.
In the above described document (2) according to FIG. 2 of that publication, the exhaust system is branched into two exhaust systems, with first and second exhaust outlet pipes 5 and 6 being respectively provided in the exhaust systems. Furthermore, an opening and closing valve 7 is provided in the first exhaust outlet pipe 5 of the respective exhaust systems. The opening and closing valves 7, 7 of the respective exhaust systems are closed when the engine is rotating at low revs, one of the opening and closing valves 7 is closed when the engine is rotating at medium revs, and the opening and closing valves of the respective exhaust systems are open when the engine is rotating at high revs. In this way, it is intended to reduce the sound pressure level of exhaust noise.
However, in the above-described document (1), a variable valve 41 is provided in an inlet of the exhaust pipe 40, which means that it is not possible to adequately reduce the sound pressure level of the exhaust noise.
Also, in the above-described document (2), the exhaust system is divided into two. A first exhaust outlet pipe 5 and a second exhaust outlet pipe 6 are provided in each of the exhaust systems, and an opening and closing valve 7 is respectively fitted in the first exhaust outlet pipe of each exhaust systems, which means that the structure is made complicated and costs also increase.
Therefore, the object of the present invention is to provide an engine exhaust assembly for a motorcycle having a simple structure, and which can sufficiently reduce acoustic noise.
In order to achieve the above described object, a first aspect of the present invention has a partitioning member provided in a pipe of a silencer arranged in the engine exhaust assembly for dividing the pipe into at least two exhaust passageways. The partitioning member is provided with a valve mechanism for causing variation in surface area of one of the exhaust passages.
For example, when the engine is rotating at low revs, the valve mechanism is closed, so that exhaust gas is discharged from the exhaust passageway without the valve mechanism. Furthermore, when the engine is rotating at high revs the valve mechanism is open so exhaust gas is discharged simultaneously from the exhaust passageway without the valve mechanism and the exhaust passageway provided with the valve mechanism. Therefore, it is expected that the exhaust noise when the engine is rotating at low revs will be reduced.
Also, by dividing one connecting pipe with a partitioning member and providing a valve mechanism in one of the exhaust passageways formed by the dividing member, the structure of the exhaust assembly is simplified.
A second aspect of the present invention is an engine exhaust assembly, having a valve mechanism for varying opening areas of a connecting pipe for a silencer arranged in the engine exhaust assembly. The valve mechanism is fitted into the connecting pipe of the silencer. One end of a connecting member connects to the valve mechanism, the other end of the connecting member connects to drive means arranged outside the silencer. Furthermore, the valve mechanism is driven by the drive means and the connecting member passes through the silencer.
The valve mechanism is fitted into the connecting pipe of the silencer, one end of a connecting member is connected to the valve mechanism, the other end of the connecting member is connected to drive means arranged outside the silencer, and the valve mechanism is driven by the drive means. Accordingly, by fitting a pipe to the silencer and housing pail of the connecting member in the pipe, the connecting member is hidden from the outside of the silencer and the external appearance of the exhaust assembly is improved.
A third aspect of the present invention is a motorcycle exhaust assembly having an engine arranged substantially in the center of a vehicle frame of the motorcycle. An exhaust pipe extending rearwards from the engine, a silencer is connected to the exhaust pipe and a valve mechanism is provided in a connection pipe of the silencer. One end of a connecting member is connected to the valve assembly, the other end of the connecting member is connected to drive means provided on the side of a vehicle frame, and the valve mechanism is driven by the drive means. Furthermore, a central portion of the connecting member is close to the silencer, and is caused to run alongside a member extending out from the vehicle frame.
The valve mechanism is fitted into the silencer, the drive means is attached to the side of the vehicle frame, and the valve mechanism is operated by connecting the valve mechanism to the drive means using the connecting member. The connecting member is close to the silencer, and is caused to run alongside a member extending out from the vehicle frame so that it reaches the side of the vehicle frame. Therefore, a member for supporting the connecting member is omitted and the number of components is reduced.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.